#include<stdio.h>
#include<math.h>
float Distance(float x1,float y1,float x2,float y2)
{
	float distance;
	distance=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
	return distance;

}
int main()
{
	float x1,y1,x2,y2;
	scanf("%f%f%f%f",&x1,&y1,&x2,&y2);
	printf("%.2f",Distance( x1,y1,x2,y2));
	return 0;
}